Every year, more than four million children are killed or disabled by diseases that can be prevented by immunization. In the proposed research project, the dynamics of childhood infectious diseases in populations with completely specified demographic structure will be modeled, the results will be compared with extant data to determine which models most accurately reflect childhood disease transmission patterns, and the implications of the introduction of immunization programs into these models will be assessed. Ultimately, the design of optimal immunization programs for developing countries will be considered, and the economic and policy implications of such programs evaluated. The long-run goal of this research is to understand how infectious diseases affect the growth and structure of human populations and conversely, how human population growth and structure influence patterns of disease transmission. Given an understanding of these phenomena, one can consider how individuals differ in susceptibility to disease, how immunization programs might be designed to take advantage of the demography of the host population, and what both the direct and indirect economic implications of immunization programs or other disease control policies might be. A number of deterministic and stochastic models describing infectious disease transmission patterns have been developed, but these models lack a realistic demographic basis and are thus ill-suited to the study of disease patterns in developing countries. In particular, the important question of how host population structure and dynamics affect disease transmission remains unaddressed The extant models also omit the issue of heterogeneity in susceptibility to infection. Little attention has been paid to how the demography of the host population modifies the effectiveness of an immunization program, and how the host population demography might be used to design more efficient immunization programs. Similarly, economic analyses of immunization programs have ignored the indirect economic effects of immunization and other health programs which result from changes in the population structure. The specific aims of this research program are to: [1] develop both deterministic and stochastic models of infectious disease transmission which incorporate fully specified human population structure and dynamics; [2] explore, using simulation studies of these deterministic and stochastic models, the effects of changes in the demography of the population on disease incidence and prevalence and on the patterns of disease transmission, and conversely, explore the effects of changes in the disease patterns in the population on host population structure and dynamics; [3] consider the design of immunization programs which incorporate the population and disease dynamics elucidated in the theoretical and simulation models; [4] analyse statistically the impact of factors which influence variation in individual susceptibility to infection; and [5] develop more complete approaches to evaluating the long-run economic effect of health-intervention programs using the information from the models,and simulation studies. Four major research projects comprise the proposed program. [1] Development of a set of mathematical models Of disease transmission which are both epidemiologically and demographically realistic and tractable, and which can be validated using extant data on infectious diseases. [2] Simulation studies of these models to explore the 'impact of variations in fertility, migration and mortality for disease dynamics, and to assess the effects of immunization programs on population structure. [3] Statistical analysis of the covariates of the force of infection using hazard models to assess the effect of the hosts's age and other independent variables on the force of infection in order to identify those groups most at risk of infection. [4] Economic analysis, based on these models, of the direct and indirect economic effects associated with the implementation of an immunization program, both as a principal health care program, and when implemented in conjunction with other health care schemes.